There is a secondary battery configured in such a manner that positive and negative electrode plates are wound or laminated with a separator interposed therebetween and they are enclosed together with an electrolyte solution in an outer case. It is known that gas occurs in such a secondary battery due to repeated charge and discharge, causing variations in internal pressure, deformation of the outer case, and others. This deformation is undesired because they cause rapid deterioration of the secondary battery. For avoiding such deformation, a flat-shaped secondary battery is particularly arranged such that binding plates or the like are placed in contact with pressed surfaces of an outer case, pressing against the pressed surfaces, to prevent deformation of the case. Further, also used is a battery pack in which a plurality of secondary batteries are arranged and externally entirely bound with binding plates.
For instance, Patent Literature 1 discloses a battery pack in which flat type secondary batteries stacked one on another are entirely narrowed by binding plates and tightened with a belt. It is disclosed that this configuration can bear down active materials applied on an electrode plate, thereby preventing separation of the active materials from the electrode plate. Another battery pack is also disclosed (see Patent Literature 2, for example) in which binding plates are placed one each between stacked secondary batteries and connected to each other to give surface pressure on each secondary battery. Any battery packs mentioned above are adapted to maintain the planarity of a side surface of the secondary battery to uniformize the surface pressure.